The present invention relates to a precrystalline intraocular implant.
It relates generally to posterior chamber intraocular implants for a phakic eye, in particular for correcting ametropias of a young patient with a clear crystalline lens.
This kind of intraocular implant is implanted between the anterior face of the crystalline lens and the iris.
The narrowness and the environment of the space between the iris and the crystalline lens give rise to problems in the successful use of this type of implant. Too strong a contact with the posterior face of the iris can lead to depigmentation thereof and rubbing on the crystalloid can cause a cataract of the crystalline lens.
Similarly, this kind of implant is affected by anterior-posterior movements of the center of the crystalline lens during accommodation for near vision, which causes problems with stabilizing and centering this kind of implant.
The posterior surface of the optic of precrystalline implants is spherical, and has a particular radius, typically 10.5 mm. This choice is advantageous from the fabrication point of view, but the anterior face of the crystalline lens when relaxed does not have a single spherical surface, but in reality an aspherical surface, with an infinite number of successive spherical surfaces.
Obviously an implant whose posterior spherical surface has only one radius is not able to espouse the anterior surface of the crystalline lens.
Similarly, the position relative to the anterior surface of the crystalline lens of precrystalline implants in which the posterior surface of the optic has a single radius of curvature is somewhat hit and miss. This results in some instability of the position of the implant relative to the crystalline lens.
Furthermore, most precrystalline implants are spaced apart from the anterior face of the crystalline lens and therefore avoid any contact with it.
WO-98/17205 describes an intraocular lens for a phakic eye adapted to be implanted between the anterior face of the crystalline lens and the iris, comprising an optical part formed on a central body and a haptic part, the posterior face of the lens having a central spherical first portion having a first radius and an annular spherical second surface portion having a second radius greater than the first radius. The radius of curvature of the central spherical first portion is much smaller than the radius of curvature of the anterior face of the crystalline lens, to reduce the probability of contact with the crystalline lens at the center. The diameter of the circumference of the haptic part is smaller than the diameter of the corresponding ciliary sulcus and the contact of the anterior face with the iris in order for the lens to be self-centering.
To this end, the present invention provides a precrystalline intraocular implant adapted to be implanted between the anterior face of the crystalline lens and the iris, the implant comprising an optical part formed on a central body without impeding accommodation and a haptic part.
According to a first aspect of the invention, the posterior face of the body includes a central spherical surface portion having a first radius, an annular spherical second surface portion having a second radius greater than the first radius, and a concentric spherical third surface portion surrounding the second portion and having a third radius greater than the second radius.
In a preferred embodiment of this aspect of the invention, the outside diameter of the peripheral ring is less than or equal to the diameter of the anterior face of the crystalline lens, and the peripheral ring therefore does not bear in the sulcus. In this case, a centered and stable position is ensured by the complementary shapes of the spherical surfaces of the posterior face of the body and the corresponding areas of the anterior face of the crystalline lens. In this embodiment, the haptic part of the concentric spherical third surface portion matches the corresponding part of the crystalline lens when relaxed. Large apertures in the haptic part protect the metabolism of the crystalline lens.
This preferred embodiment has an important advantage at the time of implantation. The implant must be released into the posterior chamber in front of the crystalline lens without worrying about placing the peripheral part in the ciliary sulcus, which the surgeon cannot see. Furthermore, because of the small thickness of this kind of implant and its small diameter, which is approximately 10 mm, the implant can be inserted through a 2 mm self-healing corneal or sclerotic-corneal incision. Finally, in this embodiment, the posterior surface of the implant espouses the interior face of the crystalline lens when relaxed in three areas with different radii, from the smallest at the center to the largest at the periphery.
According to another aspect of the invention, the peripheral ring of the haptic part is adapted to bear in the ciliary sulcus. The presence of this peripheral ring prohibits any decentering of the precrystalline intraocular implant in the posterior chamber. For this kind of implant, it is sufficient for the posterior face of the body to include a spherical central surface portion with a first radius and a spherical annular surface portion having a second radius greater than the first radius.
The haptic part preferably includes at least four radial arms of constant width and inclined toward the rear at an angle of 10xc2x0.
Thanks to the configuration of the posterior surface of the central body, the latter perfectly matches the convex shape of the surface of the anterior face of the crystalline lens, which minimizes the overall size and at the same time increases the actual surface area of contact between the posterior face of the central body and the crystalline lens.
With implants in accordance with either aspect of the invention, the radius of curvature of the anterior face of the central body, or each of the radii of curvature thereof, is calculated as a function of the ametropia to be corrected.
In one embodiment of the invention it is the whole of the body that constitutes the optical part, for example a monofocal optical part, and the anterior face of the body has a spherical central surface having a first radius and a spherical annular surface having a second radius. This kind of embodiment is particularly suitable for a convergent meniscus optic for correcting hypermetropia.
In another embodiment, it is only the central part of the body that defines the optical part, the body having a nonrefractive ring around this central part. With this kind of body, the anterior surface can advantageously be spherical with a single radius of curvature in the case of a divergent optic for correcting myopia (i.e. concave or divergent meniscus optic).
Despite the resulting close contact between the posterior face of the central body of the implant and the anterior face of the crystal lens when relaxed, aqueous humor continues to circulate between these two surfaces, in particular because of anterior-posterior movements of the center of the crystalline lens on the occasion of accommodation, which modifies the radius of curvature of the central zone of the anterior face of the crystalline lens, and aqueous humor is aspirated into the space formed in this way between the body and the crystalline lens.
To enable the implant to be inserted through a small incision, the material of which the implant is made is flexible and highly hydrophilic and has a high refractive index. This kind of implant can have a minimum thickness close to 30 xcexcm at the center of the optic for negative diopter implants for correcting myopias and 30 xcexcm at the edge of the optic for positive diopter implants for correcting hypermetropias. For the contact with the iris and the crystalloid to have no physiological effect, the surface of the implant is made as smooth as possible, for example polished to a finish of 2 to 3 nm.
According to a preferred feature of the invention, the haptic part includes a peripheral ring and arms connecting the peripheral edge of the central body to the peripheral ring.
According to another preferred feature of the invention, the haptic part incorporates large diameter apertures delimited by a pair of arms, the edge of the body and the peripheral ring. These apertures in the haptic part of the intraocular implant, situated at the periphery of the crystalline lens, facilitate good contact of the aqueous humor with the anterior face of the equatorial region of the crystalline lens, despite the presence of the precrystalline intraocular implant on the anterior face of the crystalline lens.
This is because the metabolically active areas of the crystalline lens are on the anterior face of the crystalline lens, and more particularly at its equator, where cellular multiplication occurs and crystalline fibers are synthesized.
Other features and advantages of the invention will become more apparent in the course of the following description.